Input requested for speeding up signed download URI creation

[Matt Ryan <ma...@apache.org>]

Hi oak-dev,

Creating a signed download URI itself is really fast and does not require
communication with the cloud storage service (e.g. Azure, S3) to create the
URI.  However, in the current implementation we actually make at least
three network calls when we do this:
1 and 2) When we call BinaryImpl#getUri(), we check to see if we can get a
reference [0] for the binary to ensure the binary is not inlined.  We
cannot create a signed download URI for an inlined binary obviously.
However, calling getReference() actually turns into two network calls, at
least for Azure - one to check if the blob ID exists in the blob store, and
one to get the blob properties that are needed to construct a DataRecord
(e.g. last modified time, content length).  Then the reference is returned
from this record.
3) When the data store backend creates the URI it checks to see if the
binary is actually in the cloud storage before creating the URI [1] (see
OAK-7998).  It is possible to have a Binary instance get a reference for it
even if it is not uploaded yet (i.e. it is in the cache still).

I'm looking for ways to speed this up (seek OAK-8551 and OAK-8552).  Some
questions:
* Is there a better way to see if a Binary is stored inline than trying to
get a reference for it?
* For the purposes of getting a reference, could we bypass the creation of
the DataRecord and just ask the storage backend for a reference?  If you
follow the code path you can see the creation of the DataRecord and
therefore the network calls are not actually needed to get the reference.
* Could we instead rely on the BlobIdTracker for the exists() check in the
storage backend?  This of course would require a fix for OAK-8298.

Any other ideas?


[0] -
https://github.com/apache/jackrabbit-oak/blob/2bef22fe5c8ebd69d65bb05fd457c08713f51aa4/oak-store-spi/src/main/java/org/apache/jackrabbit/oak/plugins/value/jcr/BinaryImpl.java#L96
[1] -
https://github.com/apache/jackrabbit-oak/blob/2bef22fe5c8ebd69d65bb05fd457c08713f51aa4/oak-blob-cloud-azure/src/main/java/org/apache/jackrabbit/oak/blob/cloud/azure/blobstorage/AzureBlobStoreBackend.java#L778


-MR